I need to improve my climbing. I have Friel's Training Bible (3rd ed.) and a HR monitor. To this point, I have a base so I should be good to add some specific intervals. I've already done Friels LTHR test.

Friel recommends targeting Force, Muscular Endurance and Endurance in this order. He does a nice job of describing interval workouts to target these areas; however, I'm confused about how to structure interval sets.

For example, for an Steep Hill Force Workout Friel specifies:
8% or greater grade.
Less than 2min to climb.
Up to HRZ 5b, RPE18-19 (very, very hard) This would put my HR 174-179.
In & out of saddle.
3-5min recover to HRZ1.
No more than 2x per week

How many reps should I start with? How many sets should I start with?
2min Interval + 5min Recover = 7min

This is a very hard work out so I'm guessing it should be relatively short. Maybe start with 1 set of three reps and another set in a few weeks?

BTW I picked this work out because I have a short training window for this evening.

I do these. The keys are to build - maybe start with 3-4 and work up to 6-8 - and to work for consistency. Accelerate up the hill (don't hammer for first section and then fade). Make your last interval as good as your first. The problem with doing this purely by HR is that you will fade in terms of work/effort. That is why I switched to Powertap. The non-powertap way to handle this is to use time - time yourself up your chosen hill. Try to finish all intervals within 5-10%. Once you cannot do the effort within this window you should stop. In the Allen/Coggan power training book they suggest that you should stop intervals when your power (or time) drops 10% below your 3rd interval. I only do these 1x week - on the long weekend ride I seek long hills.